Carrier 48HC 04-28 Manual

Also see for /50HC 04-28: Controls, Start-Up, Operation and Troubleshooting

Carrier 48HC 04-28 Manual Manual pdf 19 page image

19expire before another stage can be added or a stage can besubtracted. If at any time the Supply--Air Temperature (SAT) fallsbelow the Minimum Supply Air Temperature Upper Level(Configuration→COOL→SAT→SAT.U), the requested stageswill not be allowed to increase. If at any time the SAT falls belowthe Minimum Supply Air Temperature Lower Level(Configuration→COOL→SAT→SAT.L), the requested stages willbe reduced by one without honoring C.DEC. If SAT.L and SAT.Uare configured so that they are close together, the last stage ofcompressor might cycle rapidly, slowed only by its minimum onand off--time requirements.Compressor ControlThe compressor control works hand and hand with the stagingcontrol. As the staging control requests stages, the compressorcontrol determines what actual compressors are available orrunning and tries to provide stages for what is requested. Theavailability of a compressor depends on time guards, circuitdiagnostics, outdoor temperature, and the unit size.The Number of Circuits (Configuration→COOL→N.CIR)configuration tells the control how many compressors are installedon the unit. The Circuit A Lockout Temp(Configuration→COOL→CIR.A→CA.LO) and Circuit BLockout Temp (Configuration→COOL→CIR.B→CB.LO)configurations set the outdoor temperature in which the respectivecompressor is allowed to run down to. Timeguard A (RunStatus→COOL→CIR.A→TG.A) and Timeguard B (RunStatus→COOL→CIR.B→TG.B) display the time a respectivecompressor has before it is available for use. Individual circuitdiagnostic tests are performed during operation which may or maynot allow a compressor to be used. The available stages at anygiven time are displayed as Available Compressors (RunStatus→COOL →AVL.C). The actual compressors running atany given time are displayed as Actual Cooling Stages(Operating Modes→COOL→ACT.C). Compressor A (RunStatus→COOL→CIR.A →CMP.A) and Compressor B (RunStatus→COOL→CIR.B →CMP.B) are displayed on when therespective compressor is running.There are time guards to protect the compressors. Compressor MinOn Time (Configuration→COOL→MRT.C) and Compressor MinOff Time (Configuration→COOL→MOT.C) apply before acompressor can be turned back on or turned off.Outdoor Fan ControlOutdoor fans are controlled electromechanically, not directly by thecontrol system. Refer to specific unit wiring diagram and or servicemanual for details on how the outdoor fans operate. In general, theoutdoor fan is energized with compressor A or may have partialfans operate with compressor B. Humidi--MiZert units will have aMotormasterR control on some or all fans.Dehumidification ControlOn units equipped with a VFD, a simple dehumidification functionis available if not equipped with the Humidi-MiZert option.Dehumidification operation requires installation and configurationof either a space relative humidity sensor or a relative humidityswitch input. Dehumidification is a cooling mode function. Thisdehum control is set by the configuration Dehum Control noReheat (Configuration →COOL →DHUM). Dehum Control isfactory defaulted to Disable which means that any dehum demandis ignored.IMPORTANT: The HUM terminal on the field connection boardis not wired and requires an isolation relay with gold platedcontacts to wire to MBB J9-5 and 6. The RH sensor input requiresthe ECB to be installed if not already.When enabled, Dehum control will monitor the dehumidificationdemand, cooling demand, and heating demand. If a cooling call orheating call is present, the dehumidification routine will be preventedor cancelled. When just a dehumidification demand is present, thecontrol will request a Reheat2 Stage, Requested Reheat2 Stages = 1(Operating Modes →COOL →HMZR→REQ.R) and run the indoorfan at Fan Speed - Reheat2 (Configuration →I.FAN →FS.RH).During this condition the Dehumidification Active? (OperatingModes →COOL →ACT.D) status point will be yes. This willcontinue until the dehumidification demand is satisfied or a cooling orheating call is activated.Heating OperationThe 48/50HC unit’s heating operation consists of: demand, modedetermination, staging request to satisfy the demand, and handling arequest with the unit’s resources. These resources can be gas heat orelectric heat. This section covers both gas heat units and electric heatunits. The Type of Heat Installed (Configuration→HEAT→HT.TY)configuration will be factory set to 1 for gas units, 2 for electric heatunits with heaters installed, and 0 for electric heat units without heatinstalled. The unit enters a heating mode based on a demand, decideshow to satisfy the demand, executes its plan, and then leaves theheating mode.Heating Mode ControlThe heating HVAC mode (Run Status→MODE→HVAC=4),represents both types of heating (gas or electric) under all types ofcontrol. For the unit to be allowed to enter the heat mode, heatmust be enabled (HT.TY = 1 or 2), and the Outdoor AirTemperature (Temperatures→AIR.T→OAT) must be less than theHeating Lockout Temp (Configuration→HEAT→HT.LO). HeatOAT Lockout (Run Status→MODE→H.LOC) displays whenheat is locked out on outdoor temperature and therefore can notallow heat mode. The control will display if it is ok to select theheating mode (Operating Modes→HEAT →OK.HT= Yes).Thermostat ControlFor the unit to enter heating mode, three additional things must betrue: the indoor fan must be ok to use, the mode changeover timeguard must be expired, and there must be a heating demand (W1,W2). The unit will remain in heating until the heating demand isdropped or if any of the above conditions turn false. The heatingmode can not officially end until all heat stages are off and the IGCfan request is dropped (on gas units).Space Sensor ControlFor the unit to enter heating mode, five additional things must betrue: the indoor fan must be ok to use, the mode changeover timeguard must be expired, the unit must have a valid spacetemperature, the W1 jumper must be installed, and there must be aheating demand. The unit will remain in heating for at least oneminute and until the heat demand drops below --0.5_F or if any ofthe above conditions turn false. The heating mode can notofficially end until all heat stages are off and the IGC fan request isdropped (on gas units without Humidi--MiZer).Supply--Air Temperature Sensor (SAT)The SAT Heat Mode Sensing (Configuration→HEAT→SAT→SAT.H) informs the unit if the supply air sensorhas been relocated downstream of the heat section. Thisconfiguration affects the Supply Air Temperature (Temperatures→AIR.T→SAT) value displayed as listed below.When SAT.H = DSBL, the Supply Air Temperature (Temperatures→AIR.T→SAT) value on the Scrolling Marquee and the CCNtables will be forced to zero when heat outputs turn ON or OFFand for 5 minutes after. The default Supply Air Temperaturelocation is at the fan inlet, upstream of the heat section.When SAT.H = ENBL, the Supply Air Temperature (Temperatures→AIR.T→SAT) sensor reading is displayed at the ScrollingMarquee and the CCN tables during heating mode. This settingshould only be used if the original SAT sensor wires are removedfrom the Main Base Board (MBB) and replaced by an accessorySAT sensor located in the supply duct downstream of theheat section.ComfortLINK v1.X